Verifying Predictive Models for Determining Final Implant Volume in 2-Stage Implant-Based Breast Reconstruction

Most breast reconstructions following mastectomy use a 2-stage tissue expander (TE)-to-implant approach. Prior studies on prepectoral and subpectoral breast reconstructions have identified formulas for predicting final implant size using TE size and final fill. The aim of this study is to test the accuracy of these models.

A retrospective chart review of patients who underwent 2-stage TE-to-implant breast reconstruction within the Duke University Health System between 2021 and 2024 was performed. Demographic, oncologic, and reconstructive data were collected. The equations (26.6 + 0.38 * [TE final fill] + 0.61 * [TE size]) for prepectoral and (71.7 + 0.8 * [TE final fill] + 0.1 * [TE size]) for subpectoral reconstructions were used to calculate predicted implant sizes, which were then compared with actual implant sizes.

Seventy prepectoral patients (117 breasts) and 39 subpectoral patients (67 breasts) met criteria for inclusion. All patients had at least 5 months of postoperative follow-up. The mean predicted implant size was 23 cc less than the mean actual size (477 cc versus 500 cc). The root-mean-square errors for prepectoral and subpectoral reconstructions were 73.6 cc and 54.9 cc, respectively.

In general, both models underpredicted final implant size. Depending on the implant profile, a 55- to 75-cc difference equates to the models being accurate within 3 to 4 sizes for prepectoral and 2 to 3 sizes for subpectoral reconstructions, suggesting their potential use as a starting point to guide surgeon decision-making. Being able to predict final implant size more accurately will optimize surgical planning, decrease the number of implants ordered for each case, and reduce costs.